The present invention relates to a speed control system for an automotive vehicle or the like.
A control system to which the present invention constitutes a novel improvement is disclosed in U.S. Pat. No. 3,774,715 which is assigned to the same assignee as the present invention. The shaft of a speedometer type speed sensor is angularly positioned in accordance with vehicle speed. A control plate fixed to the shaft modulates an air stream in a modulator unit, the modulated air pressure being applied to a diaphragm which is connected to the vehicle throttle valve to control the vehicle speed. The desired vehicle speed is set by adjusting the pre-load of a spring which applies a restoring force to the shaft. Whereas the system operates quite well once the desired speed is set, a drawback is encountered in that precise setting of the desired speed by means of spring tension is difficult to achieve in practical application.
A recent improvement to the system comprises means for angularly positioning the assembly which forms the air stream relative to the plate for setting the desired vehicle speed. Although precise setting is accomplished by this improvement, another drawback is introduced in the form of substantially increased complexity of construction and manufacturing cost.
U.S. Pat. No. 3,441,104 discloses a mechanism comprising a U-shaped spring, a friction disc and cam which enable speed setting in a different but effective manner by momentarily actuating the cam when the vehicle is moving at the desired speed. However, the mechanism as disclosed in this latter patent converts angular movement into linear movement and involves a radial lost motion connection. It is therefore not applicable as disclosed to the present type of system in which angular movement must be transmitted rather than converted.